Backscattering spectrum of a solid cylinder next to a horizontal surface when the cylinder’s axis is not horizontal

Abstract

When a solid cylinder lies proud on horizontal sand sediment there has been progress in understanding the backscattering spectrum as a function of grazing angle and the viewing angle relative to the cylinder’s axis [Williams et al., J. Acoust Soc. Am. 127, 3356-3371 (2010)]. The resulting evolution of the target strength spectrum is sometimes referred to as the “acoustic color” or the “acoustic template.” For cylinders having identical ends and a transducer at a fixed grazing angle relative to the cylinder’s center, viewing the cylinder over a 90 degree range is sufficient for characterizing the template. If the cylinder’s axis has a vertical tilt such that one end is partially buried in the sand, then the symmetry of the template is altered and a 180 degree range is required. Some of the changes in the template can be approximately modeled using a combination of geometrical and physical acoustics. The resulting analysis gives a simple approximation relating certain changes in the template with the vertical tilt of the cylinder. A similar approximation also applies to a metallic cylinder adjacent to a flat free surface and was confirmed in tank experiments. [Work supported by ONR.]